Recently, some vehicles have been equipped with an eco-drive assist apparatus for assisting the driver in eco-drive in view of environmental protection. The eco-drive assist apparatus determines whether the vehicle is traveling efficiently in fuel economy by checking various factors, which may include the degree of depressing the accelerator pedal, the efficiency of the engine and transmission, the traveling speed and the accelerated velocity. When the vehicle is traveling efficiently in fuel economy, the vehicle is in an eco-drive state. When it is determined that the vehicle is in the eco-drive state, an LED (light emitting diode) may be turned ON. The fuel economy may be calculated at an instantaneous time in traveling and may be indicated as an instantaneous fuel efficiency.
Japanese Patent Application Publication No. 2000-205925 proposes displaying a target fuel economy expressed with a mark and an instantaneous fuel economy expressed with a bar graph on a common index and making it possible for the driver to instantaneously judge whether the instantaneous fuel economy compared with the target fuel economy is good or bad. Japanese Patent Application Publication No. 11-220808 proposes displaying the engine speed numerically in the hybrid vehicle and a distribution ratio expressing how the engine speed is distributed to traveling of the vehicle and charging of the battery.
In a case where information assisting the driver in eco-drive is displayed, the quantity of eco-drive that expresses the driving state of the vehicle is compared with a threshold value for judging whether the vehicle is in the eco-drive state, and eco-drive information on the comparison result is displayed. The driver refers to the eco-drive information and determines whether the vehicle is in the eco-drive state. In displaying the eco-drive information, it is determined whether the engine has been started up, and the result of this determination may be displayed. When the engine has been started up although the eco-drive information shows the eco-drive state, there is a mismatch between the eco-drive information and the information showing the working state of the engine. This mismatch may confuse the driver.